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88 4.3 electric fuel pump not on while running

Davidc55

New member
Hey hows it going, so I have ran into a new issue that I haven't had. My fuel pump will run with key on engine off, but once the engine is started the pump doesn't run. Just got done changing the oil pressure safety switch and the ignition switch, and all is wired correctly. Not sure why the pump isn't on with engine running. Any advice is helpful, thanks.
 
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Hey hows it going, so I have run into a new issue that I haven't had.
My fuel pump will run with key on engine off,
As you know, that would be against USCG and inner water way regs.

but once the engine is started the pump doesn't run.

Just got done changing the oil pressure safety switch and the ignition switch, and all is wired correctly. Not sure why the pump isn't on with engine running. Any advice is helpful, thanks.
As Ed suggested, the pressure switch will be a N/O style. (N/O = normally open at below 4 or 6 psi)

The fuel pump's circuit will be OPEN in the absence of engine oil pressure, and will be closed with the presence of engine oil pressure.

The start-bi-pass circuit operates the fuel pump (or fuel pump's relay) until engine oil pressure is achieved.
 
RicardoMarine, so the start bypass circuit, does it only function while the engine is being cranked over?

In 1988, the Start-bi-pass circuit would be activated via the starter motor's solenoid circuit, and yes..... only during cranking.
This is required because the N/O low oil pressure switch circuit is OPEN until approx 4 to 6 psi oil pressure is achieved.

As the solenoid becomes powered, so does the fuel pump or the pump's relay.

In other words, this bi-passes the normal circuit that would otherwise power the fuel pump either directly or via a relay.

Without the start-bi-pass circuit, we would not have any fuel pump action during cranking due to lack of at least 4 to 6 psi oil pressure.



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